Unique Keys

; llama_multi_key: per-position XOR key array, the powers of two. Position i is
; XORed with key[i] = {0x01,0x02,0x04,0x08} and compared to a stored target. XOR
; is self-inverse. Technique: per-position XOR key array. r0 = 1 on accept.
; Accept rule: nonzero.
;
; targets = 0x4D 0x4B 0x4A 0x43  ->  password "LINK"
;   'L'^0x01=0x4D, 'I'^0x02=0x4B, 'N'^0x04=0x4A, 'K'^0x08=0x43

        len   r1
        cmp   r1, 4
        jnz   bad           ; exactly 4 bytes

        mov   r7, 0
        ldb   r0, [r7]
        xor   r0, 0x01
        cmp   r0, 0x4d
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0x02
        cmp   r0, 0x4b
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0x04
        cmp   r0, 0x4a
        jnz   bad
        inc   r7
        ldb   r0, [r7]
        xor   r0, 0x08
        cmp   r0, 0x43
        jnz   bad

        mov   r0, 1
        ret
bad:    mov   r0, 0
        ret